The present invention relates to image transmission. More particularly, the present invention relates to video communication and to video communication involving cascaded stations.
Videocommunication equipment, such as videoconferencing systems and videophone devices, have enabled people to communicate visually without having to travel to a common location. As a result, videocommunication participants can be separated by large distances.
A typical videoconferencing application uses a video camera to capture images of a target, such as a meeting participant or a document. The images are encoded as a data stream and transmitted over a communications channel to a remote location. For example, the data stream may be transmitted over a phone line, an integrated services digital network (ISDN) line, or the Internet. The encoding process is typically implemented using a digital video coder/decoder (codec), that divides the images into blocks and compresses the blocks according to a video compression standard, such as the ITU-T H.263 and H.261 recommendations. In standards of this type, a block may be compressed independent of the previous image or as a difference between the block and part of the previous image.
In a typical videoconferencing system, the data stream is received at a remote location, where it is decoded into a series of images, which may be viewed at the remote location. Depending on the equipment used, this process typically occurs at a rate of one to thirty or more frames per second.
In some videoconferencing applications, it is desirable to transmit images from more than one station for display in real-time. Traditional videoconferencing standards have addressed point-to-point communications where the participants in one location are able to send and receive video, audio and data information to and from participants in a second location. Technologies have been developed to extend these point-to-point connections to allow multi-way or multi-point multi-media communications sessions, emulating the functionality of traditional audio conference calls. Early multi-point servers have allowed all participants to receive the multi-media information from one location, depending on who in the conference was speaking.
More recently, continuous-presence multi-media servers have been developed which allow multiple participants to see and hear most or all of the other participatory locations simultaneously. These continuous-presence systems have been built using a central multi-point server topology where all locations dial into a central multi-media conference server, or a network of conference servers which operate cooperatively to deliver continuous-presence style multi-media information to all participants. These central servers have been built as specialized devices. For example, one specialized device type involves videoconferencing systems built with an array of network interfaces coupled to an array of video, audio, and data decoding units. The array of video, audio, and data decoding units feed individually-decoded streams into a central bridging unit where the data is multiplexed into an appropriate composition of multiple streams and then re-encoded and sent back to each user location. These architectures require powerful computational servers and high-speed backplanes to interconnect the units. The result of this combination has been a very expensive, dedicated hardware system that, practicably, is directed to applications for central office environments.
A more recent multi-media server-type provides a switch-based architecture that simplifies the high-speed interconnect requirement of multiplexing real-time decoded raw video streams within a server environment. The architecture involves the composition of video chains to construct the composite video from multiple sources, through the use of a switch arrangement and relatively complex control software. A significant disadvantage of this architecture is that its switch-based arrangement coupled with its complex control software renders it prohibitive for many lower-cost markets, such as consumer-directed applications.
Generally, the present invention provides methods and arrangements for displaying images transmitted from multiple locations in real-time.
According to one embodiment of the present invention, a multi-point multi-media system uses off-the-shelf terminals to provide a continuous presence multi-point multi-media function. A more particular aspect of the invention allows a continuous presence server capable of supporting n streams to be constructed by interconnecting n video communications terminals on n different communications lines using standard video conferencing terminal architectures and functions (picture-in-picture).
Another particular embodiment of the invention is directed to a modular implementation, in which each of a plurality of stations has a video display and a video camera for generating a video signal. A central location includes a cascaded arrangement of signal processing units. Each signal processing unit is constructed and arranged for receiving cascaded signals, including at least one cascaded video signal, at a designated position in the cascaded arrangement. Each signal processing unit combines the video signal of an associated one of the stations with a cascaded video signal according to the designated position of the signal processing unit in the cascaded arrangement.
Other particular embodiments of the present invention are directed to methods and specific aspects relating to the above-characterized arrangement.